that plants grew with energy from the sun,
carbon dioxide from the air, and chemicals
drawn from soil, water and air until the Swiss
chemist Nicolas-Theodore De Saussure
proved it in 1804.
Once scientists understood what plants got
from soil, they were able to create solutions
containing these nutrients in the lab. This
opened up the path to creating synthetic fertilizers and, eventually, hydroponic solutions.
The nutrient-water mix in which hydroponic
plants grow is a solution. A solution is made
up of one or more solutes dissolved in a
solvent. The solvent is typically the substance
present in the largest amount (Fig. 2).
Hydroponic solutions are designed to
mimic soil, but with some improvements. “In
terms of the chemistry, soil is like a soup,
because it contains all sorts of molecules,”
explains Heiner Lieth, a crop
ecologist and hydroponics
expert at the University of
California, Davis. “But the
plant does not need all of
these chemicals to function,
so a hydroponics solution is
a streamlined version of what
you find in the soil.” Farmers,
and scientists carefully design
the hydroponic solution in
which plants grow to minimize
costs and maximize plant
Plants grow by using sunlight
and carbon dioxide (CO2) to
produce sugars, such as glucose (C6H12O6), and oxygen (O2):
6 CO2 + 6 H2O + light energy
➔ C6H12O6 (glucose) + 6 O2
In addition to carbon dioxide and water,
plants need a variety of other chemical nutrients. Plants need some of these nutrients in
large amounts and others in small amounts.
The former are called macronutrients, and the
latter are known as micronutrients. Macronutrients include nitrogen (N), phosphorus (P),
potassium (K), and calcium (Ca). Micronutrients include boron (B), copper (Cu), iron (Fe),
manganese (Mn), and zinc (Zn).
The acidity of the hydroponic solution is
also important to consider. It is measured
by checking the water’s pH, a number that
describes the concentration of hydrogen
ions (H+) in the solution. The pH range of a
hydroponic solution should generally be kept
between 5 and 7. This is important because
many nutrients react differently depending on
how acidic or basic a solution is.
For example, calcium and phosphorus are
important to plants, and they need to be available
in the solution to be taken up through the roots.
But if the solution is too basic, calcium ions
(Ca2+) will react with phosphate ions (PO43–) in
the solution to form a precipitate, hydroxyapatite
(Ca5(PO4)3OH). Once this solid forms, neither of
the ions is available to the plants.
Taste the difference...
You might expect tomatoes grown in water
to be extra juicy, or hydroponic celery to be
extra crisp. But that has not been observed.
In general, it is very hard to taste the differ-
ence, and you may have eaten hydroponically
grown produce many times without noticing
But taste is not the main challenge for pro-
ponents of hydroponics. Other obstacles need
to be overcome before the
full potential of hydroponics
can be realized. Hydroponic
farms are expensive to set
up and maintain, and they
require specialized training.
Crops are often grown in
a light-controlled environ-
ment, and water must
be pumped through the
system, both of which can
be expensive and energy-
The best way to take
advantage of hydroponics
may be to combine it with
other “green” innovations, such as solar pan-
els, as has been proposed by scientists such
as Dickson Despommier of Columbia Univer-
sity. Despommier has suggested converting
New York skyscrapers into vertical hydroponic
greenhouses, powered by solar panels and
Skyscraper farms may sound far-fetched,
but modern, industrial agriculture as we know
it today has only been around for less than a
century. This kind of farming is still relatively
new, and it is radically different from the kind
of farming that humans practiced for thou-
sands of years. Hydroponic farms may well
be the farms of the future, and many of these
advances would not have been possible with-
Figure 2. A solution
consists of a solvent,
which occupies most
of the solution, and
solutes, which are
in the solvent. In the
case of a hydroponic
solution, the solvent is
water and the solutes
consist of nutrients,
such as copper,
calcium, and potassium.
Hydroponic solutions are
that they have a uniform
Nutrient Solutions for Greenhouse Vegetable
Culture. Aggie Horticulture, Agrilife Extension,
Texas A&M University: http://aggie-horticulture.
html [accessed July 2015].
Growing Tomatoes Hydroponically: Plant Nutrition.
College of Agriculture and Life Sciences,
University of Arizona: http://ag.arizona.edu/
hydroponictomatoes/ nutritio.htm [accessed
Siegel, E. Dirt-Free Farming: Will Hydroponics
(Finally) Take Off? Modern Farmer, June 18,
[accessed July 2015].
Mallory Pickett is a science writer who lives in
La Jolla, Calif. Her latest ChemMatters article,
“The Skinny on Fats,” appeared in the April/May
William Gericke coined the term
in the 1930s. Gericke was
a scientist who studied plant nutrition at the
University of California, Berkeley, and he
is largely credited with coming up with the
idea of growing plants in water. This was
the beginning of modern hydroponics.
Top: Close-up of
one cabbage from a
showing its bare
roots. Left: Workers
tend to lettuce
grown in hydroponic